We don't directly support this yet.
For the time being, here are some suggestions that are worth exploring.
1. Using the TextTransform utility - http://msdn.microsoft.com/en-us/library/bb126245.aspx
2. Using MSBuild
- http://www.platinumbay.com/blogs/dotneticated/archive/2009/08/28/running-t4-templates-with-msbuild.aspx
- http://geekswithblogs.net/EltonStoneman/archive/2008/07/25/an-msbuild-task-to-execute-t4-templates.aspx
3. Microsoft Code Generation and T4 Text Templates discussion - http://msdn.microsoft.com/en-us/library/bb126445.aspx
A quick note, you still have to compile the generated code (.cs file) in order to use it with your project.
Hope this helps.